All of the information given on this blog is presented in an historically correct format with a constant deviation of C = 0 cents. Nonetheless, many tuning devices and programs don’t allow you to change the value of A, or give you a false impression that you are changing the value of A by letting you program a deviation for A but nonetheless transposing everything up or down so that A = a fixed frequency. Unfortunately, there is no standard, and the only way to know what your particular device/software does is to test it. If you have entered the deviation values as given here, you can test your setup by putting your device on equal temperament, recording the sound of the note C, then changing the device to an unequal temperament and comparing the sound of the note C to the one you have recorded. If they are precisely the same note (no beats), then your device works correctly. If you hear beats or wavering timbre, unfortunately you’ve got an IRT on your hands.
However, even with an irritating IRT, all is not lost. You can still force your device to give you a constant C no matter what the temperament, although you will have to change the reference pitch for A each time you change temperament (precisely as it should in fact be, since A is one of the flexible notes!). At the bottom of every temperament graph on this blog there is a series of constant C frequencies for the different “historical” pitch levels:
“French” (Haynes A -2 = 392) = 233,1
“Baroque” (Haynes A -1 = 415,3) = 246,9
“Classical” (No Haynes, A = 430) = 255,7
“Modern” (Haynes A +0 = 440) = 261,6
“High Baroque” (Haynes A +1 = 466,2) = 277,2
In the graphics on this blog, just above each C value is the A value for that particular temperament which you will have to program in order to keep C constant. For example, if you wanted to keep a constant C of 246,9 in Werckmeister’s Continuo temperament (version 1/5th Syntonic comma), you would have to program the A reference for an IRT to 413,6.